1. Field of the Invention
The present invention relates to an air or gas type accumulator for storing a hydraulic fluid under pressure within a predetermined range, by utilizing compression and decompression of a gas, and more particularly to a device and a method for detecting leakage of a precharged gas from such a gas type accumulator.
2. Discussion of the Prior Art
One known type of accumulator using a compressible nature of an air or gas is referred to as an air or gas type accumulator. This gas type accumulator stores a pressurized hydraulic fluid or oil under an elastic or spring-like action of a gas. The gas type accumulator can be divided into some subdivisions which include: a piston type wherein an enclosed space within the housing of an accumulator is separated by a floating piston into two chambers, one of which is precharged with a compressed gas, and the other of which stores a hydraulic fluid; and a bag or bladder type wherein a bag or bladder made of a synthetic rubber or other flexible material and precharged with a compressed gas is disposed within a housing, while a pressurized hydraulic fluid is stored in a space defined by the housing and the bladder. These piston and bladder or bag types of accumulator are commonly used.
Such a gas type accumulator cannot store a pressurized hydraulic fluid in a normal manner, if the precharged gas leaks from the accumulator. Therefore, it is necessary to detect an occurrence of the gas leakage. A known method of detecting the leakage of the gas uses a so-called stroke switch, as disclosed in Japanese Utility Model Application No. 61-45313 filed in the name of the assignees of the present application, which had not been laid open at the time the present invention was made. In the disclosed method, a stroke switch is activated by a movement of a piston in a piston type accumulator toward its gas chamber, by a larger amount than usual, where a precharged gas leaks from the gas chamber.
However, such a stroke switch should be sufficiently pressure-resistant and air-tight, since the switch is disposed within the precharged gas chamber or oil accumulator chamber which is exposed to a considerably high pressure. Accordingly, the stroke switch tends to be expensive. Further, the stroke switch is generally installed so as to penetrate the wall of the accumulator housing so that an output signal of the switch is fed to an external device. This arrangement requires a high degree of air tightness between the housing and the switch, and a high degree of pressure resistance of the portion of the housing in which the switch is installed. This results in an additional increase in the cost of manufacture of the accumulator.